System and Method for Mitigating Oxide Growth in a Gate Dielectric

ABSTRACT

Oxide growth of a gate dielectric layer that occurs between processes used in the fabrication of a gate dielectric structure can be reduced. The reduction in oxide growth can be achieved by maintaining the gate dielectric layer in an ambient effective to mitigate oxide growth of the gate dielectric layer between at least two sequential process steps used in the fabrication the gate dielectric structure. Maintaining the gate dielectric layer in an ambient effective to mitigate oxide growth also improves the uniformity of nitrogen implanted in the gate dielectric.

This application is a continuation of Ser. No. 11/931,529, filed Oct.31, 2007 (pending), which is a continuation of Ser. No. 11/145,674 filedJun. 6, 2005 (expired), which is a divisional of application Ser. No.10/436,848, filed May 13, 2003, now U.S. Pat. No. 6,921,703.

TECHNICAL FIELD

The present invention relates to processes for the manufacture ofsemiconductor devices and, more particularly, to the formation of a gatedielectric with a gate electrode.

BACKGROUND OF THE INVENTION

In complementary metal oxide silicon (CMOS) technology, a need toenhance the speed and increase the density of CMOS integrated circuits(IC's) has resulted in the evolution of transistor scaling, accompaniedby progressively thinner gate dielectric oxide. Reduction in thethickness of a gate dielectric provides increased drive current, withresultant increased speed. In addition, a thinner gate dielectric offersenhanced control of channel charge, thereby reducing short channeleffects. The fabrication of thinner gate oxides, however, presents gateleakage current and reliability issues. In particular, physicallythinner gate oxides exhibit gate leakage current increasingexponentially with reduction in thickness.

The leakage current can be mitigated by introducing nitrogen atoms intothe gate dielectric. One method of nitrogen atom introduction is toperform non-thermal nitridation (e.g., plasma nitridation) on the gatedielectric. Nitridation, however, introduces damage (e.g., plasmadamage) to the top surface of the gate dielectric that can extend intothe bulk of the film and result in nitrogen pile up at lower interfacefor thinner films. The damage can cause high gate leakage, thresholdvoltage shifts, or premature oxide breakdown when the devices areoperating, as well as mobility and performance reduction. Apost-nitridation high temperature (e.g., at or above 900° C.)re-oxidation (HT ReOx) can be performed on the gate dielectric tomitigate the plasma damage and improve GOI.

Exposure to air and airborne molecular contaminants, such as moistureand organics, following nitridation and/or re-oxidation of the gatedielectric can result in inadvertent oxide growth of the gatedielectric, which can increase the equivalent oxide thickness (EOT) ofthe gate dielectric. By way of example, a nitrided gate dielectric withan equivalent oxide thickness (EOT) of about 12-13 Å and containingabout 6-8% nitrogen can be formed from a starting oxide film with athickness of about 7-8 Å. Reducing the thickness of the starting oxidefilm below 7-8 Å to reduce the EOT of a nitrided gate dielectric is notpractical. An oxide film with a thickness of about 7-8 Å includes abouttwo monolayers of gate oxide atoms. A further reduction in the thicknessof an oxide film would result in a monolayer (i.e., about 4 Å) oxidefilm. Single monolayer oxide films have increased roughness compared todual monolayer oxide films. Roughness in the starting oxide film candegrade the performance of the nitrided gate dielectric. Anotherdetrimental effect of inadvertent exposure to air and airborne molecularcontaminants is increased and variable oxide growth across wafers andfrom wafer to wafer. This results in higher EOT (e.g., from AMC) for thefirst few wafers processed, especially as EOT is reduced below about 20Å.

SUMMARY OF THE INVENTION

The following presents a simplified summary of the invention in order toprovide a basic understanding of some aspects of the invention. Thissummary is not an extensive overview of the invention. It is intended toneither identify key or critical elements of the invention nor delineatethe scope of the invention. Its sole purpose is to present some conceptsof the invention in a simplified form as a prelude to the more detaileddescription that is presented later.

The present invention relates generally to a method of reducing oxidegrowth of a gate dielectric layer during formation of a gate dielectricstructure. An added advantage of the method is improved N-incorporationuniformity. The gate dielectric structure can be fabricated by forming agate dielectric on a substrate, nitridating the gate dielectric,re-oxidizing or densifying the nitrided gate dielectric, and forming aconductive layer overlying the re-oxidized or densified nitrided gatedielectric. The reduction in oxide growth can be achieved by maintainingthe gate dielectric in an ambient effective to mitigate oxide growth ofthe gate dielectric between at least two sequential process steps usedin fabricating the gate dielectric structure.

An ambient effective to mitigate oxide growth can include an inertatmosphere, such as an inert gas, that can be maintained at a pressuresubstantially below about 760 Torr but above vacuum (e.g., about 3 Torrto about 200 Torr). The ambient can be actively purged with an inert gas(e.g., N₂). Maintaining the pressure of the inert atmospheresubstantially below about 760 Torr but above vacuum, while activelypurging the inert atmosphere with an inert gas, minimizes moisture andairborne molecular contaminants (AMCs) in the ambient, which can beabsorbed by the gate dielectric. A main source of these contaminants canbe incoming wafers and wafer carriers and their desorption. Moisture andAMCs in the ambient can be effectively reduced by maintaining thetransfer pressure as high as possible with active purging. This hightransfer pressure, however, is offset by the need to raise and lower thepressure between each process performed in the fabrication of the gatedielectric structure. Reducing the oxide growth in the gate dielectricbetween processes results in the formation of a gate dielectric with asubstantially lower EOT and substantially higher nitrogen content,compared to the EOT and nitrogen content of a gate dielectric, which isformed without being maintained in an environment effective to mitigateoxide growth between process steps. Additionally, N uniformity isimproved through the thickness of the gate dielectric layer as well asacross the wafer and from wafer to wafer on which the gate dielectricstructure can be formed.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other aspects of the present invention will becomeapparent to those skilled in the art to which the present inventionrelates upon reading the following description with reference to theaccompanying drawings.

FIG. 1 is an example of a system that can be utilized to form at leastpart of gate dielectric structure in accordance with an aspect of thepresent invention.

FIG. 2 is a methodology for forming at least part of the gate dielectricstructure using the system of FIG. 1 in accordance with an aspect of thepresent invention.

FIG. 3 is a schematic cross-sectional illustration of a gate dielectricstructure in accordance with an aspect of the present invention.

FIG. 4 illustrates a schematic cross-sectional view of a substrate inaccordance with an aspect of the present invention.

FIG. 5 illustrates a schematic cross-sectional illustration of thestructure of FIG. 4 after a gate dielectric layer is formed over thesubstrate in accordance with an aspect of the present invention.

FIG. 6 illustrates a schematic cross-sectional illustration of thestructure of FIG. 5 undergoing a nitridation process in accordance withan aspect of the present invention.

FIG. 7 illustrates a schematic cross-sectional illustration of thestructure of FIG. 5 undergoing a re-oxidation process in accordance withan aspect of the present invention.

FIG. 8 illustrates a schematic cross-sectional illustration of thestructure of FIG. 7 after the re-oxidation process in accordance with anaspect of the present invention.

FIG. 9 illustrates a schematic cross-sectional illustration of thestructure of FIG. 8 after undergoing a conductive layer depositionprocess in accordance with an aspect of the present invention.

FIG. 10 illustrates a graph of the equivalent oxide thickness and flatband voltage of the dielectric layer for different methods associatedwith the fabrication of the gate dielectric layer.

FIG. 11 illustrates a graph of nitrogen concentration versus gatedielectric depth of the thick gate dielectric layer for differentprocesses associated with fabricating the gate dielectric layer.

DETAILED DESCRIPTION

The present invention relates generally to a method of reducing oxidegrowth of a gate dielectric during formation of a gate dielectricstructure. The reduction in oxide growth can be achieved by maintainingthe gate dielectric in an ambient effective to mitigate oxide growth ofthe gate dielectric between at least two sequential process steps usedto form the gate dielectric structure. An ambient effective to mitigateoxide growth can include an inert atmosphere that can be maintained at apressure substantially below about 760 Torr but above vacuum (e.g.,about 3 Torr to about 200 Torr). The ambient can also be actively purgedwith an inert gas (e.g., N₂). In one aspect, a pressure of about 10 Torrto about 100 Torr (e.g., 30 Torr) can be optimum to minimize moistureand AMCs without excessively increasing the time to raise/lower thepressure to transfer the gate dielectric structure. Maintaining thepressure substantially below about 760 Torr but above vacuum, whileactively purging the ambient with an inert gas mitigates oxide growth ofthe gate dielectric between gate formation processes. This results inthe formation of a gate dielectric with a substantially lower EOT and asubstantially higher and more uniform nitrogen content compared to theEOT and nitrogen content of a gate dielectric, which is formed withoutbeing maintained in an environment effective to mitigate oxide growthbetween process steps.

FIG. 1 illustrates an example of a system 10 operative to form at leasta portion of a gate dielectric structure in accordance with an aspect ofthe invention. The system 10 in this example includes four processchambers 12, 14, 16, and 18 for performing separate processes that areused in the formation of at least part of a gate dielectric structure ona substrate, such as silicon. The four process chambers 12, 14, 16, and18 are coupled to a transfer chamber 22 that facilitates transfer of thesubstrate between the separate process chambers during fabrication ofthe gate dielectric structure. The four process chambers 12, 14, 16, and18 and transfer chamber 22 can be maintained leak-tight duringfabrication, such that, for example, less than about 1 mTorr/min of gascan leak back into each process chamber 12, 14, 16, and 18 and thetransfer chamber 22 during fabrication. Transfer chamber 22 can bemaintained at a fixed pressure of about 3 to about 200 Torr (e.g., about30 Torr) and process chambers 12, 14, 16, 18 can be pumped down or backfilled to this pressure to transfer the wafer, on which the gatedielectric structure is formed, in or out of the process chambers 12,14, 16, 18.

The first process chamber 12 can be used in the formation of a gatedielectric layer (e.g., silicon dioxide (SiO₂) layer) over thesubstrate. The gate dielectric layer can have a thickness of about 7 Åto about 20 Å, and be formed by a wet and/or dry thermal oxidationprocessing, such as in-situ steam generation (ISSG) and low-pressure(reduced pressure) rapid thermal process (LP-RTP). It is to beappreciated that alternate methodologies can be employed to form thegate dielectric layer. For example, any suitable technique (e.g., plasmaenhanced chemical vapor deposition (CVD), thermal enhanced CVD and spinon techniques) may be employed in forming the gate dielectric layer.Examples of CVD processes that may be utilized in accordance with anaspect of the present invention, include low pressure CVD (LPCVD),plasma enhanced CVD (PECVD), and rapid thermal CVD (RTCVD). It is to beappreciated, that other types of thin film formation can be employed,such as other deposition techniques (e.g., physical vapor deposition(PVD)) and film growth techniques.

Alternate materials can be employed to provide the gate dielectricmaterial. The gate dielectric material can be SiO₂ or another suitableoxide material that can perform the operation associated with the gatedielectric material. Examples of some other materials that can beutilized as the gate dielectric layer include AlO₃, ZrO₂, HfO₂ (AlHf)O_(X), HfO₂, La₂O₃ and Y₂O₃ to name a few. Those skilled in the art willunderstand and appreciate appropriate types of deposition techniquesthat can be employed to grow suitable crystalline structures to formgate dielectric layers, such as those identified above. It is to befurther understood and appreciated that other materials also could beemployed to form the gate dielectric layer.

The first process chamber can include a vacuum-lock door 24, whichinterconnects the process chamber 12 and the transfer chamber 22.Temperature within first process chamber 12 can be maintained by one ormore heating elements 26 operative to heat the contents of the chamber12 to within a desired temperature range. For example, prior toformation of the gate dielectric layer, the temperature can bemaintained at about 500° C. to about 700° C. and during formation of thegate dielectric layer, for example by ISSG process, the temperature canbe maintained at about 850° C. to about 1050° C. Pressure within thefirst process chamber 12 can be maintained by one or more pumpingelements 28 operative to evacuate gas from the chamber to within adesired pressure range. For example, during formation of the gatedielectric layer (e.g., by ISSG), the pressure can be maintained atabout 1 to about 20 Torr.

The second process chamber 14 can be used for the introduction ofnitrogen into the gate dielectric layer by a plasma nitridation orplasma nitrided oxide process. The plasma nitridation process caninclude applying nitrogen-source gas, such as N₂, N₂O, NO, and NH₃ or amixture of a nitrogen-source gas and inert gases, such as He, Ne, Ar,Kr, Xe, and mixtures thereof, to the exposed surface of the gatedielectric layer. The plasma nitridation process or nitrided oxideprocess introduces nitrogen atoms into the gate dielectric layer, whichmitigates leakage associated with the gate device and blocks boron intothe active channel.

The second process chamber 14 can include a vacuum-lock door 30 throughwhich the substrate can be transferred between the second processchamber 30 and the transfer chamber 22. Temperature within secondprocess chamber 14 can be maintained by one or more heating elements 32operative to heat the contents of the chamber 14 to within a desiredtemperature range. Pressure within the second process chamber 14 can bemaintained by one or more pumping elements 34 operative to introduce orevacuate gas from the chamber to within a desired pressure range. In oneaspect of the invention, the plasma nitridation process or plasmanitrided oxide process can be performed in the second process chamber 14for about 3 seconds to about 60 seconds at a power of about 2 watts toabout 3000 watts and a pressure of about 5 mTorr to about 50 Torr.

The third process chamber 16 can be used for the re-oxidation of thenitrided gate dielectric, for example by rapid thermal oxidation (RTO),or post anneal or densification in an inert atmosphere, for example byRTP, or a combination of both. Re-oxidation or post annealing of thenitrided gate dielectric layer provides a thin dielectric layer withoutsurface damage and with nitrogen atoms embedded therein to facilitatethe mitigation of leakage through the gate dielectric and improvedtransistor performance, for example improved drive current, mobilityetc. The third process chamber 16 can include a vacuum-lock door 36through which the substrate can be transferred between the third processchamber 16 and the transfer chamber 22. Temperature within the thirdprocess chamber 16 can be maintained by one or more heating elements 38operative to heat the contents of the chamber to within a desiredtemperature range. For example, prior to re-oxidation, the temperaturecan be maintained at about 500° C. to about 700° C. and duringre-oxidation of the nitrided dielectric layer, for example by RTO, thetemperature can be maintained at about 900° C. to about 1050° C. A postanneal in N₂ from about 900° C. to about 1050° C. could be applied.Pressure within the third process chamber 16 can be maintained by one ormore pumping elements 40 operative to introduce or evacuate gas from thechamber 36 to within a desired pressure range. For example, duringre-oxidation (e.g., RTO) of the dielectric layer the pressure can bemaintained at about 0.5 Torr to about 50 Torr.

The fourth process chamber 18 can be used in the formation of aconductive layer, such as polysilicon, over the re-oxidized, nitridedgate dielectric. If the conductive layer is comprised of polysilicon,the conductive layer may be formed using any suitable techniqueincluding chemical vapor deposition (CVD) techniques, such as lowpressure chemical vapor deposition (LPCVD) or plasma enhanced chemicalvapor deposition (PECVD). If the conductive layer is comprised ofamorphous silicon, germanium, or their combination, standard depositiontechniques may be employed. If the conductive layer is comprised of ametal, standard sputtering techniques may be employed.

The fourth process chamber 18 can include a vacuum-lock door 42 whichinterconnects the process chamber 18 and the transfer chamber 22.Temperature within the fourth process chamber 18 can be maintained byone or more heating elements 44 operative to heat the contents of thefourth chamber 18 to within a desired temperature range. For example,during formation of the conductive layer (e.g., by CVD) the temperaturecan be maintained at about 500° C. to about 800° C. Pressure within thefourth process chamber 18 can be maintained by one or more pumpingelements 46 operative to introduce or evacuate gas from the chamber 18to within a desired pressure range. For example, during formation of theconductive layer (e.g., by CVD) the pressure can be maintained at about250 Torr to about 350 Torr.

The transfer chamber 22 interconnects the process chambers 12, 14, 16,and 18 and provides an interface between the process chambers 12, 14,16, and 18 during fabrication of at least part of the gate dielectricstructure. The transfer chamber 22 can include one or more cool-downchamber (not shown) to allow cooling of the gate dielectric betweenfabrication processes. Load locks 48 can be provided to allowintroduction and removal of a substrate from the transfer chamber 22.

The transfer chamber 22 contains an ambient, such as an inertatmosphere, which comprises an inert gas (e.g., N₂, He, Ar, Kr, Xe andmixtures thereof). Pressure within the transfer chamber 22 can bemaintained by one or more pumping elements 50 operative to evacuate gasfrom the chamber to within a desired pressure range. For example, theinert atmosphere can be maintained at a pressure substantially belowabout 760 Torr. The inert atmosphere can also be maintained at apressure above vacuum levels (i.e., mTorr levels). Additionally, a gasdistribution system 52 can be in fluid communication with the transferchamber 22 for actively purging the ambient of the transfer chamber 22.By “actively purging” it is meant that the inert gas can be introducedinto the transfer chamber 22 at a rate effective to continuouslyevacuate the atmosphere of the transfer chamber 22. By way of example, aflow rate effective to continuously evacuate the atmosphere of thetransfer chamber 22 can be about 2 liters per minute to about 7 litersper minute. The inert gas used for purging can include any inert gas,such as N₂, He, Ar, Kr and Xe, and mixtures thereof, as well as otherinert gases and mixture thereof which do not detrimentally affect (e.g.,oxidize) the gate dielectric during transfer.

Maintaining the pressure of the inert atmosphere of the ambientsubstantially below 760 Torr but above vacuum, while actively purgingthe ambient, can establish a uniform, laminar gas flow within theambient. This uniform, laminar gas flow can provide sufficient drag toevacuate airborne molecular contaminants (AMCs) (e.g., moisture andorganics) from the ambient. Airborne molecular contaminants canpotentially be absorbed by the gate dielectric and cause oxide growth ofthe gate dielectric.

In one aspect, the inert atmosphere can be maintained at a pressure ofabout 3 Torr to about 200 Torr (e.g., 30 Torr) while being activelypurged by a gas having a flow rate of about 2 liters per minute to about7 liters per minute (e.g., 5 liters per minute). At a pressure of about3 Torr to about 200 Torr, residual moisture and organics from theprocesses used to form the gate electrode structure can be readilyevaporated and be evacuated from ambient by the inert gas. Residualmoisture and organics can be diluted by operating at higher pressures,for example, about 10 fold as pressure is increased from about 3 toabout 30 Torr. Atmosphere pressures below about 3 Torr are difficult tomaintain during active purging gas and do not readily facilitate theestablishment of a uniform, laminar gas flow, which has sufficient dragforce to evacuate airborne molecular contaminants. Atmosphere pressuresabove about 200 Torr decrease the rate at which moisture and organicscan be evaporated and are substantially higher than at least some of thepressures used for the processes. An optimum operating pressure can beabout 10 to about 100 Torr (e.g., about 30 Torr) and can reduce levelsof moisture and organics without excessively prolonging time to bringprocess chambers up or down to transfer chamber pressure to allow wafertransfer.

FIG. 2 illustrates a methodology of fabricating a gate dielectricstructure using the system described above. The methodology begins at100 such as in connection with providing and preparing a substratematerial, such as silicon. At 110, the substrate can be introduced intothe system by transferring the substrate through the load lock into thetransfer chamber. The transfer chamber contains an inert atmosphere,which throughout the fabrication process, can be maintained, forexample, at a pressure of about 3 Torr to about 200 Torr, a temperatureof about 20° C. to about 30° C., and can be actively purged with aninert gas, such as N₂, at a flow rate of about 2 liters per minute toabout 7 liters per minute.

The substrate can be transferred from the transfer chamber into thefirst process chamber, which can be evacuated, for example, to apressure of about 1 Torr to about 20 Torr. At 120, a gate dielectric canbe formed overlying the substrate. By way of example, the gatedielectric can be formed using an ISSG process at a temperature of about850° C. to about 1050° C.

Following formation of the gate dielectric at 120 and once pressure isequalized to that of the transfer chamber, the gate dielectric can betransferred from first process chamber into the transfer chamber. At130, the substrate can be cooled within the transfer chamber, forexample, to a temperature below about 150° C.

Following cooling at 130, the substrate with the overlying gatedielectric can be transferred into the second process chamber, which isthen evacuated, for example, to a pressure of about 15 Torr to about 50mTorr. At 140, nitrogen can be introduced into an exposed surface of thegate dielectric. By way of example, the nitrogen can be introduced intothe gate dielectric by plasma nitridation (PN). The nitrided gatedielectric can then be transferred from second processing chamber,through the transfer chamber, into the third process chamber.

At 150, the nitrided gate dielectric can be re-oxidized or densified toremove any plasma damage to the layer. By way of example, there-oxidation can be performed by RTO at a temperature of about 900° C.to about 1050° C. and a pressure of about 0.5 Torr to about 50 Torr.

After re-oxidation at 150, the gate dielectric can be transferred fromthe third process chamber, through the transfer chamber, and into fourthprocess chamber. At 160, a conductive layer, such as polysilicon, can beformed over the gate dielectric and substrate. The conductive layer canbe formed for example by chemical vapor deposition (CVD) at atemperature of about 600° to about 800° C. and a pressure of about 200Torr to about 300 Torr.

FIG. 3 illustrates a transistor device 210 (e.g., MOSFET device) havinga gate dielectric structure 214 in accordance with an aspect of thepresent invention. The transistor device 210 can be fabricated on asubstrate 212, such as silicon. The transistor device 14 includes a thingate dielectric layer 216 (e.g., about 8 Å to about 20 Å oxide layer).It is to be appreciated that the transistor device 210 is provided forillustrative purposes and that the substrate can include a plurality oftransistor devices.

The gate dielectric layer 216 can be an oxide (e.g., silicon dioxide(SiO₂)) or any other dielectric material suitable for operating as agate oxide of a transistor device. Since the gate dielectric layer 216is relatively thin (i.e., less than 20 Å) nitrogen atoms 218 areintroduced into the dielectric layer 216 to suppress leakage currentsassociated with the operation of the transistor device 210. The nitrogenatoms 218 can be introduced into the dielectric layer 216 by a plasmanitridation or plasma nitrided oxide process. The plasma nitridation,however, causes a damaged (e.g., plasma damaged) surface layer of thegate dielectric layer 216 or through the bulk of the oxide layer.

A re-oxidation or densifying process can be performed on the damagedlayer to provide a gate dielectric layer 216 substantially withoutdamage and with nitrogen atoms 218 embedded therein to facilitate themitigation of leakage of the transistor device 210. The re-oxidation onplasma nitrided oxide removes plasma damage from plasma nitrided oxide,and minimizes nitrogen loss during a subsequent fabrication processes aswell as improves MOSFET performance, for example drive current andmobility.

The transistor device 210 can also include a gate electrode 20 that canbe disposed over the gate dielectric layer 216. The gate electrode 220can be comprised of polysilicon, amorphous silicon, germanium, or metal.Sidewall spacers 222 of a suitable insulating material can be disposedadjacent to the sidewalls of the gate electrode 220. A source region 224and a drain region 226 can also be formed in the substrate 212.

The source and drain regions 224 and 226 can also include source/drainextensions (not shown) that extend to regions generally aligned with andpartially beneath the edges of the gate electrodes. Those skilled in theart will understand and appreciate that the transistor can be either a Ptype or N type transistor. The source and drain regions 224 and 226 canbe formed as N or P type regions by doping with boron, arsenic or otherappropriate doping materials, as known in the art.

FIGS. 4-9 illustrate a methodology of fabricating a part of a transistordevice in accordance with an aspect of the present invention. Referringto FIG. 4, a substrate layer 250 that can be formed from a semiconductormaterial, such as silicon or polysilicon. The substrate layer 250,however, could be formed from any materials such as gallium arsenide,germanium, silicon-germanium, epitaxial formations, silicon carbide,indium phosphide, silicon-on-insulator substrates (SOI), strained Sisubstrates, and/or other semiconductor substrate materials.

FIG. 5 illustrates the substrate 250 after an oxidation process isinitiated to form a gate dielectric layer 254 (e.g., silicon dioxide(SiO₂) layer) over the substrate 250. The gate dielectric layer 254 canhave a thickness of about 7 Å to about 15 Å, and be formed by a wetand/or dry thermal oxidation processing. In one aspect of the invention,the gate dielectric layer can be formed using an ISSG process in whichthe substrate 250 is heated to a temperature of about 850° C. to about1050° C. in an atmosphere maintained at a pressure of about 1 Torr toabout 20 Torr for about 5 to about 60 second.

After formation of the gate dielectric layer 254 over the substrate 250,nitrogen can be introduced into the gate dielectric layer 254. FIG. 6illustrates the introduction of nitrogen into the gate dielectric layer254 by a plasma nitridation or plasma nitrided oxide process 300. Theplasma nitridation process or nitrided oxide process 300 introducesnitrogen atoms 255 (FIG. 7) into the gate dielectric layer 254, whichmitigates leakage associated with the gate device. In one aspect of theinvention, the plasma nitridation process or plasma nitrided oxideprocess can be performed for about 3 seconds to about 60 seconds at apower of about 2 watts to about 3000 watts and a pressure of about 5mTorr to about 50 Torr. The plasma nitridation may also cause plasmadamage to the layer 256 (FIG. 7). The plasma damage to the layer 256 cancause high gate leakage, threshold voltage shifts, or premature oxidebreakdown when the devices are operating.

Following introduction of nitrogen into the gate dielectric layer 254,the gate dielectric layer can be re-oxidized or densified, for exampleby rapid thermal oxidation (RTO). FIG. 7 illustrates a re-oxidationprocess 310 being performed on the damaged surface layer 256 to providea thin dielectric layer 258 without plasma damage (FIG. 8) and withnitrogen atoms 255 embedded therein to facilitate the mitigation ofleakage of the transistor device. By way of example, the re-oxidation310 on plasma nitrided dielectric layer 256 can be performed at atemperature of about 400° C. to about 1200° C. for about 1 to about 60seconds, at a pressure of about 1 to about 50 Torr with a gas havingabout 1% to about 100% of an oxygen-source, such as O₂, N₂O, and NO inan inert gas, such as He, Ne, Ar, Kr, Xe and N₂. The re-oxidationprocess 310 can be performed in a rapid thermal processing (RTP) chamberor an oxidation furnace.

After re-oxidation of the nitrided gate dielectric, a conductive layer260 can deposited (e.g., by chemical vapor deposition (CVD) techniques)over the resultant structure to provide the conductive gate electrode ofthe gate structure. FIG. 9 illustrates the gate structure after theconductive layer is deposited over the resultant structure.

During transfer of the gate dielectric between processes used in theformation of the gate electrode structure (e.g., between the initialoxidation process and the nitridation process, between the nitridationprocess and the re-oxidation process, and/or between the re-oxidationprocess and the deposition process), the gate dielectric can bemaintained in an ambient, such as an inert atmosphere that includes aninert gas (e.g., N₂, He, Ar, Kr, Xe, and mixtures thereof). The inertatmosphere can be maintained at a pressure substantially below about 760Torr. The inert atmosphere can also be maintained at a pressure abovevacuum levels (i.e., mTorr levels). The ambient can be actively purgedwith an inert gas. In one aspect, the inert atmosphere can be maintainedat a pressure of about 3 Torr to about 200 Torr (e.g., 30 Torr) whilebeing actively purged by a gas with a flow rate of about 2 liters perminute to about 7 liters per minute (e.g., 5 liters per minute).

Maintaining the pressure of the inert atmosphere of the ambientsubstantially below about 760 Torr but above vacuum, while activelypurging the ambient, mitigates oxide growth of the gate dielectricduring transfer of the gate dielectric between processes. Reducing theoxide growth of gate dielectric between processes results in theformation of a gate dielectric with a substantially lower EOT, improveduniformity, and substantially higher nitrogen content compared to theEOT and nitrogen content of a gate dielectric, which is formed withoutbeing maintained in an environment effective to minimize oxide growthbetween processes.

FIG. 10 illustrates a graph 400 comparing the equivalent oxide thickness(Å) (represented by triangles) and flat band voltage (Vfb) (representedby squares) of gate dielectric layers fabricated by different methods.For each fabrication method, the equivalent oxide thickness and flatband voltage were measured after an in-situ steam generation process(ISSG), a plasma nitridation process (PN), a re-oxidation process (RTO),and a polysilicon deposition process (POLY) have been performed on asilicon substrate. The fabrication methods differed in that betweenprocesses of some methods the gate dielectric electric was maintained inambient effective to mitigate oxide growth (e.g., an inert atmospheremaintained at 30 Torr and actively purged with an inert gas at a flowrate of about 5 liters per minute), as opposed to being exposed to anair atmosphere. Processes, which are referred to in the graph as being“clustered”, are processes between which the gate dielectric layer wasmaintained in ambient effect to mitigate oxide growth. Processes, whichare referred to in the graph as being “un-clustered”, are processesbetween which the gate dielectric layer was exposed to an airatmosphere.

As illustrated in the graph 400, fabrication methods that include atleast two processes that were clustered formed dielectric layers withsubstantially lower equivalent oxide thicknesses than the fabricationmethod that did not include any clustering. For example, fabricationmethods in which the ISSG, DPN, RTO, and POLY were all clustered showedan about 12% to about 13% equivalent oxide improvement (i.e., about 1.1to about 1.5 reduction in equivalent oxide thickness) compared to thefabrication method which was un-clustered. Even in fabrication methodswhere only two process were clustered (e.g., ISSG and DPN, DPN and RTO,and RTO and POLY), an improvement in equivalent oxide thickness wasobserved compared to fabrication methods in which the processes wereun-clustered. This improvement in EOT was achieved without a decrease inflat band voltage.

FIG. 11 illustrates a graph 450 of nitrogen concentration versus gatedielectric depth of a thick gate dielectric layer (e.g., plasma nitrided10 Å oxide layer) for different processes associated with fabrication ofa gate dielectric. The nitrogen concentration was measured using acommercially available Time of Flight-Secondary Ion Mass Spectrometer(TOF-SIMS). A first indicator 452 references data points (represented bysquares) associated with nitrogen concentration in a dielectric layerversus depth after an in-situ steam generation process, a plasmanitrided process, and a re-oxidation process has been performed on asilicon substrate. Between each of these processes, the gate dielectriclayer is exposed to air. A second indicator 454 references data points(represented by triangles) associated with nitrogen concentration in adielectric layer versus depth after an in-situ steam generation process,a plasma nitrided process, and a re-oxidation process has been form on asilicon substrate. Between each process, the gate dielectric layer wasmaintained in ambient effective to mitigate oxide growth (e.g., an inertatmosphere maintained at 30 Torr and actively purged in an inert gas ata flow rate of about 5 liters per minute).

As illustrated in the graph 450, substantially more nitrogen (i.e.,about 30% more N) was incorporated in the gate dielectric layer when thegate dielectric layer was maintained in an ambient effective to mitigategrowth between processes compared to air. This increase in nitrogenenhances the dielectric quality (e.g., mitigates leakage) of thedielectric layer. In comparison to a gate dielectric with same level ofnitrogen that is formed using an un-clustered process, a gate dielectriclayer formed using a clustered process showed improved performance at areduced EOT. In addition, for oxide films about 10 Å to about 20 Å,graphs similar to 450 show flatter N profiles (with improved dielectricreliability) and improved N uniformity across the wafer and from waferto wafer.

Those skilled in the art will appreciate and understand that althoughthe gate dielectric in the system and methodology described above ismaintained in an ambient effective to mitigate oxide growth duringtransfer of the gate dielectric between the four fabrication processes,the gate dielectric could be maintained in the ambient between just twosequential processes. Additionally, although the dielectric in thesystem and methodology described above is transferred through the sametransfer chamber between fabrication processes, the gate dielectriccould potentially be transferred through separate transfer chambersbetween sequential processes. At least one of the separate transferchambers could include an ambient effective to mitigate oxide growth ofthe gate dielectric.

Those skilled in the art will also understand and appreciate thatvarious processing operations that can be utilized in formation oftransistors in accordance with an aspect of the present invention. Byway of example, the gate electrodes can be patterned viaphotolithography and etched (e.g., via an etch chemistry or plasmaetching) to form the gate electrode structures. Ion implantation orother doping techniques can be utilized to form source/drain regions 224and 226 (FIG. 3). It further is to be appreciated that the gateelectrode structures can be used in the formation of CMOS, BiCMOS or HBTdevices.

What has been described above includes examples and implementations ofthe present invention. Because it is not possible to describe everyconceivable combination of components, circuitry or methodologies forpurposes of describing the present invention, one of ordinary skill inthe art will recognize that many further combinations and permutationsof the present invention are possible. Accordingly, the presentinvention is intended to embrace all such alterations, modifications andvariations that fall within the spirit and scope of the appended claims.

1. A processing system for use in forming at least part of a gatedielectric structure on a substrate, comprising: a first process chamberfor forming a gate dielectric layer over the substrate; a second processchamber for introducing nitrogen atoms in the gate dielectric layer; andan interface with an ambient of uniform, laminar inert gas flow betweenthe first process chamber and the second process chamber.
 2. Theprocessing system of claim 1, the interface comprising a transferchamber, the transfer chamber including an atmosphere being maintainedat a pressure substantially below about 760 Torr but above vacuum andbeing actively purged with an inert gas.
 3. The processing system ofclaim 2, the atmosphere being maintained at a pressure of about 3 Torrto about 200 Torr.
 4. The processing system of claim 2, the atmospherebeing actively purged at a flow rate of about 2 liters per minute toabout 5 liters per minute.
 5. The processing system of claim 2, furthercomprising a third processing chamber for performing a re-oxidation ordensifying process.
 6. The processing system of claim 5, furthercomprising a fourth process chamber for forming a conductive layer overthe re-oxidized or densified gate dielectric layer.
 7. A processingsystem for forming a gate stack of a transistor, comprising two processchambers connected by a transfer chamber, the transfer chamber having ansubstantially oxidant-free ambient of uniform, laminar inert gas flowbelow 760 Torr.
 8. The processing system of claim 7, in which thepressure of the transfer chamber is about 3 to 100 Torr.
 9. Theprocessing system of claim 8, in which the pressure of the transferchamber is about 30 Torr.
 10. A processing system for forming a gatestack of a transistor, comprising: a first process chamber for forming agate dielectric layer over the substrate; a second process chamber forintroducing nitrogen atoms in the gate dielectric layer; and a transferchamber with an ambient of uniform, laminar inert gas flow between thefirst process chamber and the second process chamber, said transferchamber including a gas distribution system and one or more pumpingelements.